1. Field of the Invention
The present invention relates generally to an optical waveguide fiber having a dispersion zero shifted to higher wavelengths, and particularly to such a fiber that has negative total dispersion.
2. Technical Background
In response to demands for high performance waveguide fibers having properties compatible with particular communications systems, investigation of segmented core optical waveguide refractive index profiles has continued. For example in U.S. Pat. No. 5,483,612, Gallagher et al., (the '612 patent) there is disclosed a core profile design which provides low polarization mode dispersion, low attenuation, a shifted dispersion zero, and low dispersion slope. Other core refractive index profiles have been designed to meet the requirements of applications that include the use of higher power signals or optical amplifiers.
A problem that can arise when a core profile is altered in order to arrive at a desired property is that the property is realized at the expense of one or more other essential properties. For example, a certain core refractive index profile design may provide lower total dispersion slope, thus allowing for wavelength division multiplexing over an extended wavelength range. However, in achieving low total dispersion slope, attenuation may be seriously compromised, or cut off wavelength can be moved out of an acceptable range.Thus, core profile design is an exacting task, in which model studies usually precede the manufacturing stage of product development.
There is a need in the art to continue the study of refractive index profiles in order to better understand interaction among profile variables and thus to arrive at profile variable combinations that provide optical waveguide fibers having a set of desired properties.